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Estimating ceramic cap ESR

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Oznog

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Well, I have a project with a moderately high current driver with pretty tight space concerns and the SMD tantalum I put in there isn't doing well. Getting quite hot.

I'm considering just going with one of the high capacitance ceramic, even that tant was pressing the available space pretty hard. Now in the past I've worked on the assumption that the ESR is "too low for it to matter" but I'm not familiar with these tiny high cap ones. Like I'm looking at the C2012Y5V1A106Z 10uF 10V Y5V in an 0805 pkg. However its spec sheet gets no more specific than "Owing to their low ESR and excellent frequency characteristics, these products are optimally suited for high frequency and highdensity type power supplies." This is often the case.

What should I reasonably expect for ESR here? Looks like 0.1 ohm might be an absolute max. 0.01 ohm would be "so low we don't care anymore".
 
I think politicians wrote that data sheet.

The equivalent circuit for a cap is R - j(1/ωC).
If you have a sample, raise the ω into the cap until the Z levels off. This must be your R = ESR.
You can at least find it for the tantalums, and then twice the ESR gives twice the temp. rise above ambient.

Another way is to estimate the surface area for the cap and find a resistor with the same surface area. If it's a one watt resistor, dissipate one watt into the resistor and measure the temp. rise above ambient for the resistor and for the cap.
This gives your Θc-a in °C/w and so you can figure how many watts the cap is using up.

I once got a logic databook from TI which advertised "high speed".
There was not a single number relating to speed on any of the datasheets; the space for these values was blank.
How gullible are engineers supposed to be? Or maybe they are testing exactly that?
 
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Download Kemet spice. It has impedance curves for all Kemet capacitors (ceramic and tantalum) up to 10MHz. It shows reactive, resistive, and total impedance components.

Edited to Add: Attached is what KEMET spice shows you for a 10uF X5R 16V capacitor.
 

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Y5V has very bad voltage coefficient of capacitance too. A 25V Y5V may only exhibit 20% of its rated capacitance at 25V. X5R will usually keep about 80% of its capacitance at full rated voltage.

The Kemet spice program allows you to change bias voltage and temperature to see the effects on any particular capacitor.
 
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